In a method for drawing a stereoscopic image as the prior art, an integral imaging (Hereinafter, it is called “II”) system is well known. In this system, each pixel of a plurality of images (multi-view image) having a parallax is dispersedly positioned on one image (Hereinafter, it is called “elemental image”). By controlling an orbit of a light from each pixel (composing the elemental image) with a lenticular lens, an observer can perceive a stereoscopic image (the II system is called “integral photography system”). This II system is known as an ideal method for drawing a stereoscopic image regenerated with nearly actual light. However, in the II system, a resolution of the image is low because each pixel of a plurality of images is dispersedly positioned on one elemental image.
Accordingly, one-dimensional II system, which prevents the resolution from lowering by assigning a parallax along a horizontal direction of the elemental image, is proposed. In this one-dimensional II system, a coordinate (x,y,z) of each vertex of a drawing object (three-dimensional CG model) is multiplied with a perspective projection matrix. After that, values of y-coordinate and z-coordinate are respectively divided by 1−z/d (d: a center of projection). As a result, a value along the horizontal direction (x-coordinate) is subjected to a parallel projection, and a value along the vertical direction (y-coordinate) is subjected to a perspective projection.
In JP-A 2004-257124 (Kokai), above-mentioned method, i.e., a value along the horizontal direction is subjected to the parallel projection and a value along the vertical direction is subjected to the perspective projection, is disclosed (Hereinafter, it is called “a first method for drawing a stereoscopic image”). However, another method, i.e., a value along the horizontal direction is subjected to the perspective projection and a value along the vertical direction is subjected to the parallel projection, is not disclosed (Hereinafter, it is called “a second method for drawing a stereoscopic image”). Accordingly, a stereoscopic image cannot be drawn by switching the first method for drawing a stereoscopic image and the second method for drawing a stereoscopic image.